[RTL UI] update widgets and apps for UI mirroring

Small tweaks all around to handle UI mirroring:
- swap existing symbols like arrows, or use alternative ones
- rotate some images, like chevrons and dogear icons
- flip some left and right swipe handling
- flip some geometry arithmetic like tap on left or right
  side of page or dict window
- use new ProgressWidget:getPercentageFromPosition() instead
  of geometry arithmetic
- BD.wrap() some concatenated string bits, like in reader
  and menu footers
- flip inverse_reading_order when UI is mirrored

More specific tweaks:
- ReaderGesture: reset some specific gestures when UI direction
  has changed (tap on top/bottom left/right corners, for
  bookmarks and FileManager "Plus menu").
- ReaderRolling: show markers on the correct side of page,
  in single or dual page mode.
- KoptOptions: swap left and right icons in Alignment toggle
- CheckMark: proper rendering in all 4 mirroring/rtl combinations.
- VirtualKeyboard: forbid any mirroring
- Move util.getMenuText into Menu.lua

frontend/ui/widget/sortwidget.lua

@@ -1,3 +1,4 @@
+local BD = require("ui/bidi")
 local Blitbuffer = require("ffi/blitbuffer")
 local BottomContainer = require("ui/widget/container/bottomcontainer")
 local Button = require("ui/widget/button")
@@ -452,14 +453,15 @@ function SortWidget:onPrevPage()
 end
 
 function SortWidget:onSwipe(arg, ges_ev)
-    if ges_ev.direction == "west" then
+    local direction = BD.flipDirectionIfMirroredUILayout(ges_ev.direction)
+    if direction == "west" then
         self:onNextPage()
-    elseif ges_ev.direction == "east" then
+    elseif direction == "east" then
         self:onPrevPage()
-    elseif ges_ev.direction == "south" then
+    elseif direction == "south" then
         -- Allow easier closing with swipe down
         self:onClose()
-    elseif ges_ev.direction == "north" then
+    elseif direction == "north" then
         -- no use for now
         do end -- luacheck: ignore 541
     else -- diagonal swipe